With the advent of semiconductor devices having increasingly large component densities, the removal of heat generated by these devices has become an increasingly challenging technical issue. Moreover, device miniaturization has led device designers to integrate previously separate components, such as the components used to create a cache for a microprocessor, into the microprocessor die. This consolidation of devices has resulted in high CPU core power densities, and extreme power dissipation requirements.
The use of boiling/vaporizing methods with inert cooling fluids provides cooling levels that can meet extreme cooling requirements. While pool boiling (i.e., submerging a chip in cooling fluid) provides significant gains over traditional air cooling, spray cooling (i.e., spraying the chip with cooling fluid) presently provides the highest heat dissipation levels for a heat-generating device such as a semiconductor chip. The best results are obtained when the cooling fluid is uniformly sprayed over each area having a uniform dissipation requirement. The mass flow rate of sprayed cooling fluid should be at a level such that the energy needed to vaporize the sprayed cooling fluid matches the power dissipation requirements of the device.
With reference to FIG. 1, in a single, high-dissipation, spray cooling system, an inert spray cooling fluid from a reservoir 11 is preferably sprayed by a group of one or more sprayers 13 onto an aligned group of one or more chips 15 mounted on a printed circuit board 17. The cooling fluid preferably vaporizes, dissipating heat from within the chip. The sprayers, the chips and the board are mounted within an evacuated and sealed case 19 fixed within a computer system. The sprayed cooling fluid is typically gathered and cooled within a condenser 21, and then routed back to the reservoir by a pump 23. For semiconductor devices, low boiling point fluids such as 3M® FC-72 (FED. CIR.-72, i.e., FLUORINERT®, sold by 3M® Corporation), 3M's Novec line of fluids (HFE 7100, etc., sold by 3M® Corporation) or PF-5060 are among a number of known suitable cooling liquids. These fluids provide vaporization temperatures in appropriate ranges, while not having corrosive effects on the relevant materials, and not conducting electricity to any significant level (i.e., any level that would affect the operation of a submerged chip).
Modern systems using high-dissipation chips frequently have a variety of chips requiring different levels of cooling, only some of which are extreme. Depending on an electronic system's design, components containing these chips can be located throughout the system. Because they have high dissipation requirements, the chips are not easily cooled using conventional air-cooling. Because the chips are spread out, they are not easily cooled by high-dissipation spray cooling systems, which are typically complex systems. Such cooling systems will typically require either the expense of providing separate components for each individual cooling system, or the expense of interconnecting a group of cooling systems to one or more shared components (e.g., shared pumps, condensers and/or reservoirs). Therefore, high-dissipation cooling systems can be expensive and complicated to implement in complex systems having numerous hot components.
The nozzle design is a key component of spray cooling. Pressure assisted and gas assisted nozzles are known designs. However, these types of nozzles are limited in their ability to control the mass flow rate at which they spray. Therefore, they can cause “pooling” (i.e., a buildup of liquid on the cooled device due to excessive spray rates), which decreases spray cooling effectiveness.
Additionally, pressure-assisted spraying requires one or more high pressure pumps that provide a precise pressure to pump the liquid through a nozzle, even at varying flow rates. Both the distribution and the flow rate of the sprayed liquid can change with variations in the driving pressure and/or small variations in the nozzle construction. Thus, the cooling system is a sensitive and potentially expensive device that can be a challenge to control.
Gas-atomized spraying requires the delivery of both cooling fluid and a pressurized gas to a spray head in a precise manner. Because the gas must be pressurized separately from the cooling fluid, such systems are not typically closed systems, which invites contamination. Thus, both types of spray cooling system are sensitive and potentially expensive devices that can be a challenge to control.
Furthermore, spray cooling systems typically include on both active sprayer systems and active condensing systems (i.e., sprayer systems and condensing systems relying on moving parts) to operate. If either system fails, the cooling system likely becomes inoperative, potentially leading to the failure and destruction of the cooled component(s).
Accordingly, there has existed a need for a spray cooling system that can be reliably implemented, both efficiently and cost effectively, in multiple locations within a complex system. Various embodiments of the present invention satisfy these and/or other needs, and provide further related advantages.